Streszczenie This paper presents the carrier based discontinuous space vector pulse width modulation (DSVPWM) for two-phase four-leg voltage
source inverters (VSI) fed resistive and inductive loads. This proposed technique is focused on the switching losses and output current ripple
reduction in each phase-leg of inverter which does not depends on the lagging and leading power factor load. In addition, the carrier based
DSVPWM is modified from conventional two-phase four-leg VSI by replacing the zero space vector in each switching sequence. This proposed
discontinuous modulation strategy has 180 degrees for unmodulated region. Experimental results provide the performance comparison between the
discontinuous SVPWM (DSVPWM) and the traditional continuous SVPWM (CSVPWM) techniques to confirm the reduction of switching losses and
output current ripple at high modulation index. The experimental results show that total average values of normalized switching losses of the
DSVPWM and the CSVPWM are 7.908 and 11.174, respectively in which the proposed DSVPWM can reduce the switching losses from the
conventional CSVPWM up to 29 percent.Słowa kluczowe: Two-phase four-leg inverter, Switching losses, Ripple current, Discontinuous space vector pulse width modulation.
Abstract W artykkule opisano nieciągła technikę modulacji szerokości impulsu DSVPWM zastosowaną w dwufazowych czterogałęźnym
przekształtniku VSI obciążonym indukcyjnością i rezystancją. Projekt zakładał ograniczeniu strat przełączania i zafalowania prądu.
Eksperymentalnie porównano zaprojektowany układ z tradycyjnym układem ciągłym. Keywords: przekształtnik dwufazowy, nieciągła modulacja szerokości impulsu DSVPWM.
An increase of performance of the three-leg voltage
source inverter can be enhanced by reducing the switching
losses and output ripple current when the discontinuous
space vector pulse width modulation (DSVPWM) technique
for high modulation index has been performed [1-3]. Many
types of DSVPWM techniques such as DPWMMIN,
DPWMMAX, DPWM 0, DPWM 1 and DPWM 2 of threephase
voltage source inverters (VSIs) depend on types of
power factor load. For example, DPWM 0 is suitable for a
leading power factor load and DPWM 2 is fit for a lagging
power factor load [4]. In addition, three-leg voltage source
inverters can be applied to two-phase induction motor of
both of the asymmetrical and symmetrical parameter types
for industrial application [5]. Especially, the two-phase fourleg
voltage source inverter fed two-phase motors drive has
an advantage of a lower DC bus voltage requirement
compared to the DC bus voltage of two-leg and three-leg
VSI at the same output voltage of inverter [6]. On the other
hand, a disadvantage of four-leg VSI is more number of
switching devices than two and three-leg VSI. Therefore, to
reduce the switching losses in switching devices in each
leg, the modulating function of DSVPWM technique for twophase
four-leg inverter fed balanced R-L load is proposed
in this study. The experimental results of a decrease of
switching losses and output current ripples for the proposed
DSVPWM modulation are compared with the conventional
CSVPWM.
Fig. 1. A proposed two-phase four-leg voltage source inverter
Table 1. Switching state and corresponding active space vector
SV1
SV2
SV3
SV4
SV5
SV6
SV7
SV8
SV0
SV9
2Vdc
2Vdc
[...]

Introduction
At the beginning of the Match 2011 the European
Commission presented a document titled: “A Roadmap for
moving to a competitive low carbon economy in 2050". It
contains a long - term plan for carbon dioxide emission
reduction. When implemented it is expected to cause 80%
reduction in greenhouse gases emission by 2050. A vast
group of scientists claims that that way the worst
consequences of the global warming could be avoided.
The Kioto Protocol originally expired in 2012. However
all attempts to sign a new agreement have been failing from
COP 14 (Poznan, Poland, 2008), to COP 17 (Durban, RSA,
2011). After long negotiations on COP 17 the new
agreement term was set for 2015 and Kioto Protocol
extended to 2020.
In Warsaw, November 2013, another United Nations
Climate Change conference, COP 19, took place. It was
participated by representatives from about 200 countries.
Each of them was given a task to develop a plan for
achieving a low carbon economy according to the European
Commission Roadmap. The plans were presented on the
following COP 20 (Lima, Peru, 2014) and the foundation for
the new agreement was made.
In Paris, December 12th 2015, on COP 21 in Paris the
new climate agreement, called The Paris Agreement was
made. The main goal was set to keep the global warming
below 2°C, and preferable 1.5°C [1] (see figure 1).
The participant countries would aim to balance the CO2
and other greenhouse gases emissions emissions with their
removal, including forest absorption in the second half of
the 21st century. The reduction of the CO2 content via forest
absorption leads to other positive side - effects, such as the
improval of the water and soil quality as well as saving the
biodiversity and wildlife migration prevention. The Paris
Agreement is the first in the history document that obligates
all the countries among the world to aim for the climate
protection.
The Polish Prime Minister Beata Szydło submitt więcej »

In power electronics, bidirectional (four-quadrant)
switches (BDS) are a necessary part of all matrix converters
which allow to convert AC voltage directly (without a DC
link) to AC voltage with controllable amplitude and
frequency. BDS are capable to conduct current in both
directions and block voltage of both polarities. There are
several configurations of BDS but the most commonly used
is antiparallel connection of two RB-IGBT and its main
advantage is that the current is passing only through one
semiconductor [1]. Nowadays, GaN BDS begin to appear
as a single package device with dual gate and are used in
matrix converters (MC), e.g. [2, 3], but they are still not
available on the market. GaN HEMT could be a competition
for RB-IGBT due their lower switching and conduction
losses, their high frequency operation which could increase
the power density of MCs [3]. GaN HEMT connected in
series has not yet been tested as a BDS which was the
main reason to conduct the research.
I. Four-step semisoft current commutation method
A. Analysis
The 4-step semisoft current commutation method for
BDS was firstly proposed in [4]. It is called semisoft,
because half of the commutation process is soft switching
and half is hard switching [1]. There are many other
modifications of that method, e.g. 3-step, 2-step. [5] which
are the modification of the 4-step method. To analyse all the
commutation processes in a 3-phase MC it is enough to
consider only a 2-phase to 1-phase (2f/1f) converter with a
DC voltage source and RL load (Fig.1). RC snubbers
added to each GaN HEMT significantly reduce the voltage
ripple [6], (it is worth mentioning that in [2] for GaN BDS an
RCD snubber with 4 diodes, resistor and capacitor is
proposed, which could be compared in future work).
Control strategy of the 4-step current commutation
method is shown in Table 1. For example, if we want to
switch from conducting TAa to open TBa BDS and the current
of the RL więcej »

Oil-paper insulation, typically used in the power
transformer, both during normal operation and during
electrical or thermal disturbances decomposes. During this
process, gases are generated (H2 - hydrogen, CH4 -
methane, C2H6 - ethane, C2H4 - ethylene, C2H2 - acetylene,
CO - carbon monoxide and CO2 - carbon dioxide) which
partially remain dissolved in the oil.
Experience shows that the amount and composition of
gases dissolved in oil allows to conclude about the
occurrence of a defect in the transformer and its type.
General information on the decomposition product of the oil
insulation formed during different types of fault are given in
Table 1. If the defect comprises the cellulose insulation
carbon monoxide and carbon dioxide are also appear.
Since taking an oil sample from a working transformer and
then determining the type and amount of dissolved gases is
a simple and cheap procedure, their analysis (marked with
the acronym DGA) is the basic method of diagnosing the
technical condition of the transformer.
Tab. 1. Decomposition product of the oil insulation formed during
different types of fault [1, 2]
Fault type Gases
Partial discharges H2, CH4 (C2H4, C2H6)
Discharges H2, C2H2 (CH4, C2H4)
Thermal faults CH4, C2H6, C2H4, H2
In parentheses are given the gases associated in small
quantities.
On the occurrence of a defect, one concludes by
comparing the currently measured values of gas
concentrations with typical values. Typical values are
determined on the basis of statistical analysis of gases
dissolved in oil of transformer groups with common
characteristics (e.g. on-load tap-changer). The intensity of
the defect can be assessed to a certain extent by
comparing the changes in gas concentration values
between consecutive measurements with the typical values
of such changes. Typical values of changes in gas
concentrations over time are also determined for similar
groups of transformers using statistical analysis. An więcej »

Reactive power is of great importance for the operation
of the AC power system. A power system consists of
different elements. Some of them can be modelled as the
electricity containers, such as coils and capacities. Since
the AC circuits imply continually electric current and voltage
changes, these containers constantly store and release
energy. During a specific time period, the total energy
consumption of these components equals zero. The energy
flowing between the elements for energy storage does not
perform useful (active) work, but that reactive energy is
inevitably a part of total energy, together with the useful
(active) energy, which feeds the load. However, the flow of
this energy is required in order to retain the required change
of the magnetic and electrical fields of these energy
containers. The energy flowing as the reaction to the activity
of these elements is called reactive power. Despite the fact
that the energy does not perform any useful work, it is still
important for maintaining the stability of the system
operation. Maintaining a balance between consumption and
generation of reactive power has been the subject of
numerous scientific papers since the commencement of
commercial use of EPS.
Simulation of the operation of the non-linear load with
the active power filter in the programme package
MATLAB simulink
The programme package MATLAB Simulink simulates
the operation of the non-linear load to the purpose of the
analysis of the impact of the dynamic reactive power
regulation by application of the active power filter. The
model was created in line with the theory of the momentary
power values. Fig. 1 shows the simulation model of the
reactive power dynamic compensation of the non-linear
load in the
MATLAB Simulink. The power supply source is shown
through the three phase source of the sinusoidal voltage,
with effective value of the interphase voltage of 400 V. The
phase windings are star-coupled, wh więcej »

Technological advancement contributes to the increase of
applications of high-speed electrical drives.
Drives with high-speed motors are used in a wide range
of manufacturing industries including machine industries,
car manufacturing, model making, dentistry, military
industry as well as in devices producing electrical energy
from biogas or steam, to mention just a few. The ideal high
- speed motor should be small in size, have high
performance, be simple to operate and reliable. Currently
mass produced high-speed motors have speeds of about
20 - 30 000 rpm.
Permanent Magnet Brushless Direct Current motors
(PM BLDC), are particularly efficient where high-speed
applications are involved. The PM BLDC motors are
characterized by a relatively simple design, high specific
power, relatively small dimensions, a low moment of inertia
and good dynamic properties [18]. They are smaller and
require simpler control circuits than induction motors. PM
BLDC motors are also very reliable which makes them
particularly suitable for high-speed applications [6].
Motors used in high-speed electrical drives
It is commonly assumed that high-speed motors are
motors working at a speed exceeding 10 000rpm [1, 2]. The
authors of the present paper, however, are of the opinion
that a distinction should be made for motors of a lower,
medium and higher speed ranges. It is therefore suggested
that motors having power within the range of a few kilo
watts should be distinguished as follows:
􀁸 Lower speed range, including motors with speeds
ranging from 10 000 - 40 000 rpm;
􀁸 Medium speed range, including motors with speeds
ranging from 40 000 - 70 000 rpm;
􀁸 Higher speed range, including motors with speeds
ranging from 70 000 - 100 000 rpm.
Motors with speeds exceeding 100 000 rpm should be
named ultra-high-speed motors.
Currently the most popular high-speed motors are:
􀁸 Electromagnetic synchronous motors;
􀁸 więcej »

energy sources become more popular since
the last decade due to some efforts on mitigating global
warming from the use of conventional energy sources for
power plants. One of the popular renewable energy sources
is wind energy, where it is reported in JRC Wind Energy
Status Report 2016 Edition that there are about 430 GW
wind turbine generators have been installed worldwide till
2016. Within all types of wind turbine generators, Doubly
Fed Induction Generator (DFIG) become the most type
installed worldwide which dominate about 64% of market
share in 2015 [1]. This fact is based on the advantages of
DFIG in terms of technical aspect where DFIG could supply
some amount of reactive power to the grid as it is equipped
with power electronics that connected directly to the grid
and rotor side. With about 33% capacity of power
electronics, the cost of the DFIG system becomes cheaper
than its main rival in the same class, Full Converter Wind
Turbine Generator (FCWTG) type [2]. A typical model of a
DFIG can be seen in Fig 1.
Fig.1. Typical Configuration of A DFIG
When wind turbines generators (WTGs) connected to
the grid, there are some parameters must be complied to
avoid the disconnection of WTGs to prevent any damages
on the WTGs. For instance, voltage profile at the point of
common coupling (PCC), rotors and stators' current, DClink
voltage (for DFIG and FCWTG), etc [3]. A DC link as
shown in Fig. 1. is obligated to maintain the transfer energy
between the rotor and grid [4]. DC link power electronic that
links a grid side converter (GSC) and a rotor side converter
(RSC) are very sensitive with any faults, most of the wind
turbine generator manufacturers recommended the safety
margin voltage level on DC link that allowed the converters
standstill is between 0.25%-1.25% [3]. Therefore any
voltage profiles of DC-link that violate the safety range, the
internal protection of the converters should block the
converters and lead to więcej »

The growing demand of energy and the successive oil
shocks since the 70s have demonstrated the economic and
geopolitical risks of energy production based on the
exploitation of fossil fuels, whose reserves are unevenly
distributed and exhaustible. Renewable energy is the
energy comes from natural resources such solar energy,
wind, rain, tides, geothermal heat and various forms of
biomass .These resources are renewable and can be
naturally replenished continuously [1-3]. Therefore,
development of new forms of energy sources must take a
huge consideration as solution in order to cover the future
demands and the huge disturbances. Wind energy source
is regarded as one of the most important renewable energy
source; it can be used today in many applications [4]. Due
to previous, many countries have made great progress in
wind power technology such as Denmark which produces
40% of its electricity from wind, and at least 83 other
countries around the world are using wind power to supply
their electricity grids. The global wind power capacity
expanded 16% to 369,553 MW. As shown in fig.1.Although
several advantages of wind turbine, its random nature of
wind and nonlinear characteristic (Power-speed) are the
main drawbacks. Therefore, the wind turbine system must
be designed to operate at their maximum power for different
conditions. So over the last few decades, considerable
progress has been made in the MPPT techniques and
consequently many Maximum Power Point Tracking
(MPPT) methods have been developed [6-10 ].
Fig.1. Global wind power cumulative capacity [5]
The doubly feed induction generator is widely used in
variable speed wind turbine systems owing to their ability to
maximize wind power extraction and to their capability to
fulfill the basic technical requirements set by the system
operators and contribute to power system security [11-12].
Usually, a DFIG wind turbine is shown in Figure 2.
Fig.2. Wind Turbine System
A lo więcej »

Non-destructive techniques are used widely in the
industry and science in order to control and evaluate the
quality of materials without causing damage [1]. The most
commonly used NDT methods are ultrasonic testing (UT),
radiography (RT) and eddy current testing [2] .
Eddy Current Testing (ECT) is the standard and one of
the most extensively used nondestructive technique
method of electric conductivity and magnetic permeability
related property in conductive materials in order to evaluate
them [1,3]. Whose main applications are found especially in
the inspection of aircraft and nuclear industries [4,5], power
plants and other engineering constructions [6].
Eddy Current sensors can be made to operate in
differential [7] and absolute mode [8]. ECT gain interest in
of simple, fast and noncontact testing [9].
Stochastic Finite Element Method SFEM is an extension
of the classical deterministic approach for the solution of
stochastic problems. It has received considerable attention,
due to the rapid development of computer simulation,
mathematical modeling and scientific computing to predict
and understand the behavior of physical engineering and
electromagnetic devices [10,11,12].
The Monte Carlo method is powerful, popular and easy
to understand and implement, it is often used in the
literature as a reference method in order to check the
accuracy of other approaches. It has a large field
applications such as analyzing complex problems,
development of new material, industrial engineering,
simulation of physical process and analysis of nonlinear
inverse problems [10,13,14].
Various parameters induce change to the properties of
the materials over time which is still in operation, not
defective. It’s why in this work we assume the defect as a
lack of material, corrosion, imperfections of fabrication
process or aging. To take in account the effect of random
physical properties in defects areas by coupling Monte
Carlo method więcej »

The recent evolution in radiofrequency (RF) devices and
integrated circuit technologies greatly expanded the number
of wireless applications [1]. This expansion generated a
growing demand for semiconductor manufacturers,
requiring a higher integration in RF circuits. However, as
passive device performances are directly tied to their
geometry (especially for inductors), they end up being the
bottleneck on radiofrequency circuitry integration.
Inductors are of utmost importance in radiofrequency
integrated circuits [2]. These devices are employed in
critical building blocks of radiofrequency integrated circuits
such as intermediate frequency filters [2], low-noise
amplifiers [3], voltage-controlled oscillators [4], and power
amplifiers [5]. Current on-chip spiral inductors suffer from
large parasitic and area for a meager value of inductance
and quality factor [6]. The need to overcome these issues
has led to the development inductors with new geometries
housing magnetic cores that show an enhanced inductance
compared to the air core coil.
In this paper, the behavior of solenoid inductors is
systematically studied and the impact of the geometrical
parameters on its inductance and quality factor. The
principal object of my paper is to detail all the phases of
design and modeling of a solenoid inductor in order to attain
its realization and integrate it into a micro-converter [7]. This
structure increases the quality factor value while reducing
the constituent dimensions with a small manufacturing cost
[8].
Design of solenoid inductor
A simple solenoid inductor consists of a metal wire
wound around a magnetic core, as shown in figure 1 [9].
Geometric parameters used in the schematic of an
integrated solenoid inductor are as follows: the number of
turns of the coil N, length of the coil lc, length of the
magnetic core (air core) lm, spacing between turns s, width
of the magnetic core wm, width of the air core wa, width of
coi więcej »

There are many possible factors causing variation in
length or in cross-section area of an electric arc in electric
or power devices. They can be divided into distortion factors
and control factors. Among the external causes of arc
length variations, the following are the most common:
changes of the electrode positions, inflection of the plasma
column due to a transverse gas flow, inflection of the
plasma column due to a transverse magnetic field, shifts if
electrode spots due to mechanical or magnetic factors.
External factors causing variation in the cross-section area
of the arc column include: variation in the pressure of the
gas atmosphere, variation in the composition of the plasma
gas, variation in the speed of gas flowing around the arc
column, constricting the plasma by the walls of the channel
or of the plasma generator.
Varying the arc length is the most common and
important method used to influence the arc stability in
power switches and thermal power in electrothermal
devices. The arc column size in power switches should
change as fast as possible. When electrodes or plasma jets
are immersed in the furnace chamber with sufficiently high
speed, this enables fluent changes of the voltage and
consequently of the contribution of the thermal power
components in the arc energy balance [1, 2].
There are many difficulties that have to be overcome in
the modelling of an electric arc of variable geometrical
parameters. These difficulties arise due to nonlinear
dependences among the electrical, thermal and geometrical
characteristics of the plasma column [1, 3].
The Voronin model of the arc column with variable
geometrical parameters and with heat dissipation
processes dependent on the arc lateral area
In order to construct the Voronin model [4, 5] it is
necessary to adopt the following simplifying assumptions:
1. The arc column is cylindrical with a constant crosssection
area at any point along the axis;
2. Plasma is więcej »

In these days "Smart" is as a very popular term. It
usually refers to different products with an increasing
degree of computing power. Smart products such as smart
phone, smart TV or other smart electronics with a variety of
features and applications are now very popular. Electricity is
currently a strategic "raw material" and its importance in the
future years is clearly growing. For this reason, increasing
emphasis is placed on the stability, safety and security of
the electricity supply to end customers. Therefore, the
computerization is increasingly being introduced into the
electricity system during the time. Very popular is also the
new term "Smart Grid".
Despite the high popularity of this term, it is not always
clear what is meant by it. Smart Grid is often referred to as
the network of the future, a network capable of providing a
high proportion of distributed production. During the time
Smart Grid has almost attracted the attribute of a magic
wand able to solve all the problems associated with
renewable energy sources connected to the distribution
network while reducing the final price of electricity for
customers. Among the many definitions available, Fereidon
P. Sioshansi's statement is the most interesting and he
interprets the term Smart Grid as follows: "Smart Grid is the
best thing we can, but we do not know what it is."
The many of projects, articles and publications focus on
theme of Smart Grid, as well as foreign and domestic
conferences. Despite the great popularity, there is a wide
inconsistency in the definition of this term. Nevertheless,
Smart Grid is often referred also to as the network capable
of using more renewable energy sources and distributed
production than the current network.
Comprehension of the current Smart Grid network is
rather difficult and from costs perspective expensive. It is a
long-term process that binds capital over many years.
Therefore, it requires a strong commitment więcej »

The power theory of electrical systems has been
evolving continuously for more than a century, beginning
with the works of Steinmetz [1]. A significant milestone in
this direction was the introduction by Professor S. Fryze of
active current concept [2,3]. This concept served as a main
theoretical basis for constructing active and passive filtering
devices [4]. With the development of the elemental base of
power semiconductor devices and signal processors, the
control strategies of active filters developed in the direction
of ensuring minimal power losses, unity power factor and
maximum efficiency [5-9]. These strategies were based on
new provisions of the theory of power, concerning the
decomposition of currents and powers with giving physical
meaning to the individual components. A critical review of
these theoretical positions, carried out in [5-10] and many
others, suggests that the main component of the current
decomposition is the active current in the Fryze form, and
the sum of the squares of the power components is the
square of the apparent power using the Buchholz formula
as product of rms values of line currents and line-to-neutral
voltages.
The independence of the Fryze's active current and
Buchholz's apparent power from the ratio of cable
resistances is doubtful that it is correct for four-wire systems
(Fig. 1) with non-zero neutral current. The determination of
the apparent power of a three-phase power supply system
considers the limitations at which the active power is
maximized, as an allowable value of the power losses
caused by the flow of consumed currents [10]. This value is
proportional to the square of the rms value of the consumed
line currents, which appear in the Buchholz apparent power
formula, only in a three-wire power system with identical
values of the active resistances of the line wires. Especially
this difference is manifested in a three-phase four-wire
power system, where the active resista więcej »

The atmosphere pollution resulting from industrial
development, especially in the second half of the foregone
century, led to the series of greenhouse gas emission
reduction agreements in the second half of the 90s,
including the Kioto Protocol, December 1997. However the
protocol came into power after its approval by 55 countries,
including Poland, that is on February 16th 2005. It was
never approved by China and USA, world’s largest
polluters. The Kioto Protocol was valid until 2012. Despite
that no subsequent agreement was made on any of the UN
COPs (United Nations Conference of Parties) preceding the
expiration date: from UN COP 14 (Poznan, Poland, 2008) to
COP 17 (Durban, RSA, 2011) [1].
Conferences of Parties (COPs)
On December 12th, 2015, on COP 21 in Paris the world
climate agreement was established by the representatives
of almost 200 countries. Its main target is to stop the global
warming way below 2°C, preferably 1.5°C [2]. The Paris
Agreement gives the world a chance for a balanced
development. In contrast to the Kioto Protocol the efforts for
CO2 and other greenhouse gases content reduction is done
simultaneously in two ways: by the reduction of their
emission due to new technologies as well as their capture
by forests. The Paris Agreement is the first international
agreement that obliges all countries among the world to act
for climate protection. Polish prime minister, Beata Szydlo,
signed the agreement on October 7th, 2016.
By the time of the next COP 22 the agreement was
adopted by: China, USA, Brazil, Canada, Mexico, and
following EU countries: Poland, Austria, France, Germany,
Hungary, Malta, Portugal and Slovakia. The fact that Poland
was among few EU countries that adopted the act allowed
for its standalone representation on COP 22 that took place
in Marrakesh (Morocco), October 7th-18th 2016. Poland
actively participated in the Parties to the Paris Agreement
(CMA) negotiations. It especially p więcej »

In principle, the power system (PS) is related to the
process of converting primary energy sources and
consumers as users of converted energy. So far, the energy
conversion process has been carried out with applied
technology which is now able to convert natural resources
into a type of energy that can be used through a series of
certain processes in the generating unit. On the other hand,
power systems are prepared with various levels of
electricity network services to form interconnection
networks that connect generating units and load centers. In
general, an integrated network power system (INPS) is
widely used to integrate all sections [1], [2]. At present,
INPS is a large network and consists of complex integrated
companies and operators to control operations [3]-[6]. In
general, this system is used to maintain the availability and
adequacy of sustainable energy as long as customers use
utilities [7]-[11]. In addition, this network is also used to
combine all generating units located close to various
primary energy sources. In addition, this network is also
connected to the load center at different distances for power
delivery.
Nowadays, the INPS is displayed by integrating a local
power grid (LPG) to increase the guarantee of
performances [12]-[15]. On the other hand, LPG continues
to look for applied technologies as well as acceptable for
the operation. Technically, LPG is operated in the
classification structure which is used to supply power
demands in accordance with the connections at backbone
systems [2]. In particular, customers are growing faster with
increasing power demand, thus, it is requiring a different
generation system area with the addition of a power plant.
To cover this condition, the power balance must be
acceptable for energy producers and users with a
reasonable low cost [16]-[19]. Increased PS operation that
is guaranteed based on LPG performance is an important
aspect of the level of system de więcej »

Power losses in electrical grids represent one of the
essential indicators of effectiveness. The power losses in
electrical grids are the difference between power generated
by power plants and power consumed by customers. The
losses occur in power transformer and power lines,
especially when transmission energy over long distances.
Voltage control noted of power system it allows to solve
the following main tasks [1, 2]:
- balancing between generation and consumption;
- providing the required voltage level at the terminals
(outputs) of consumers of electric energy.
There is voltage regulation on the longitudinal and
transverse directions. Providing the required level of voltage
at the terminals of consumers of electric energy is solved
mainly by longitudinal regulation [2, 3, 4].
The existing centralized management system prevents
many active objects from appearing in the network. The
basis in the centralized system is the control center, where
the modes of operation of all control objects are determined
[3, 5]. When a new object or a change in the desire of the
subjects, it is necessary to reconfigure the system, which is
a very time-consuming process.
The emergence of distributed means of voltage
regulation in the network, belonging to different subjects,
having their own goals of regulation, determines the need
for a qualitatively new solution to the problem of voltage
regulation in electric networks. It is necessary to develop
new methods to control the modes of operation of power
supply systems, including distributed generation. Currently,
worldwide attention is paid to the creation of intelligent
power supply networks (Smart Grid).
In high and medium voltage networks, there are large
power flows, accompanied by significant losses. The
problem of reducing power losses during transmission can
be solved through transverse voltage regulation.
The problem of voltage regulation can be solved by
adjusting the power factor więcej »

Introduction
The most important characteristic feature that
distinguishes investment in the power sector from other
branches of industry is that it is a long-lasting and
complicated process. This is related to a relatively long life
of the elements of the power system. Polish distribution
networks include elements which have been heavily
exploited and require replacement or modernization [1-3].
Another feature typical of investment in the power industry
is a relatively long period of return on invested capital.
Besides, the capital expenditure and cost of investment are
also relatively high. Table 1 presents the age structure of
selected elements of the power grid for the five biggest
Polish distribution companies (OSD) as of end of 2017 [4].
Table 1. Age structure of selected network elements [%]
Network elements
> 40
years
old
25-40
years
old
10-25
years
old
< 10
years
old
HV overhead 42 34 15 9
HV cable 0 3 17 80
HV/MV substations 30 33 20 17
HV/MV transformers 19 33 19 29
MV overhead 37 39 17 7
MV cable 16 24 28 31
MV/LV substations 28 32 22 19
MV/LV transformers 15 29 25 31
LV overhead 31 35 21 13
LV cable 13 25 31 31
The necessity of making investment in the power
industry is motivated mostly by the fact that the
transmission and distribution networks include worn-out
elements and are largely ineffective, with high loss and low
reliability. About 25% of the network equipment is more
than 40 years old, and another 25-30% is over 25 years old.
The directions of development for the distribution
network are as follows [5-10]:
- reducing energy loss in distribution transformers and
networks,
- modernizing and expanding the 110 kV distribution
network and networks of lower voltages with a view to
the following:
o minimizing technical and commercial loss,
o increasing reliability,
o expanding the network in order to offer
services to a greater number of customers,
o connecting renewable en więcej »

Supervisory Control and Data Acquisition (SCADA)
systems play a key role in monitoring industrial processes.
Due to bidirectional connection with Programmable Logic
Controllers (PLCs) and Remote Terminal Units (RTUs),
SCADA systems are able to track process’s parameters as
well as alter required levels of parameters or even levels
triggering alarms. This makes SCADA system a very
tempting target for cyber attacks.
The most popular way of restricting access to systems
or applications is the requirement to authenticate the user
using login and password. To enhance the security of the
user authentication process, more than one authentication
factor can be used. To log in to the application, alongside
something the user knows (login and password), the user
must be in possession of something like a token or one-time
password generator, and also has to prove his identity by
using biometric methods. It seems that the mobile phone is
a perfect choice for "something that the user has" as it can
be multi-factorial in many ways with additional layers of
security, as well as many sensors embedded in nowadays
smartphones (such as a camera, fingerprint reader, iris
scanner, etc.)
To make the security solution complete, it should be
convenient for the user as well as secure. To achieve the
required level of convenience, SCADA systems could
incorporate one of a Single Sign-On technology to make
logging in process seamless with logging in to PC.
Possible implementations of Multi-Factor Authentication
(MFA) as well as Single Sign-On (SSO) technologies will be
described in the following sections.
Single Sign-On technologies
Single Sign-On is a technology of sharing authentication
or authorisation token between applications. User has to log
in once and then access to any connected application is
granted automatically because one application can
automatically send the appropriate authentication or
authorisation token in the background. więcej »

Railway turnouts are part of railways used to change the
direction of travel of a rail vehicle from the main track to
another track (branch) or vice versa. They are key elements
of railways which are exposed to negative weather
conditions such as snowfall, snow drifts, low temperature or
sleet. Disadvantageous winter conditions may block
turnouts and cause problems with traffic operation. Effective
protection assures good performance of turnouts and
contributes to efficiency and safety of rail traffic.
Currently the most common heating system for railway
turnouts in Europe is electric resistance heating system
(eor) (Fig.1).
Fig.1. Heating systems of rail turnouts
Providing a power of 330W per running meter of the rail
in the eor method gives good effectiveness of heating rail
turnouts during the heating period. Under average
atmospheric conditions (i.e. at temperature down to -20°C)
with average snowfall with currently used 330W/m heaters
eor efficiency ensures correct operation of heated turnouts.
The efficiency of heating turnouts means the ability of
heating systems to be removed from all critical elements of
snow switches and icing in a sufficiently short time. At the
same time the energy consumed for this purpose should not
be excessively large. Many factors influence the heating
efficiency such as: ambient temperature, the intensity of
snowfall, the intensity of snow blowing by wind and passing
trains, speed, number and length of passing trains, wind
speed, air humidity, installed heating power per 1 mb of rail,
the cross-section and shape of the radiator and its
arrangement on the rail, quantity and quality of the holders
fixing the radiators, efficiency of separation transformers,
weight of rails, turnout construction, dehydration of the
turnout, etc.
A typical diagram of electric resistance heating system
of rail turnout is shown in Figure 2. It employs electric
heaters of power between 300-350W/m and the supply więcej »

The intense development of the provision of electricity
supply services has resulted in the fact, that pursuant to
Act [1], referring to the regulation of the Minister of Economy
[2], there is a requirement, that the power distributor
guarantees a certain power standard.
If at the point of common coupling (PCC) (the border
between the power distributor and the power consumer), the
acceptable boundaries for parameters determining the power
quality is exceeded, the consumer may claim compensation
for poor power quality and may claim improvement of power
quality (unless the problem of poor power quality in the contract
between the power consumer and the power distributor
has been solved differently). If the source of disturbance is
not the power consumer, then the power distributor should locate
the disturbing load and reduce the emitted disturbance,
to increase the power quality at the PCC of the complaining
power consumer.
One of the most common disturbances in the power grid
today are voltage fluctuations. According to the standard [3],
this phenomenon can be defined as fast changes of the rms
value or the maximum value of voltage. Voltage fluctuations
affect the operating state of electricity loads [4], in particular
light sources. Voltage fluctuations, depending on the type of
sources, cause nuisance light flicker. This is a serious factor
that reduces the quality of human life. In unfavorable conditions,
the light flicker deepens depression or induces epileptic
states. Therefore, limiting the nuisance of flicker is an important
diagnostic work, which requires the location of voltage
fluctuation sources, i.e. indication of the point of supplying
the disturbing load [5].
To aided the location of voltage fluctuation sources, onepoint
methods are used (e.g., correlation of Pst changes
and power and/or current, examination of the interharmonic
power flow direction, analysis of voltage fluctuations [6, 7,
8, 9, 10, 11], assoc więcej »

This work is considered to the problem of the response
time of instrumentation with saving of sensitivity in
electrochemical measurements. As authors [1] claims “The
ability to measurement nA to pA currents at nanosecond
timescales remains a challenge." It is a traditional problem
of engineers that is a decrease of measurement current
range and response time, i.e. an increase current sensitivity
of a potentiostat and an enlarge bandwidth for an analytical
signal is. To save the current sensitivity of potentiostat for
higher signal time resolution the reduction of a charge
registration limit is asked that is limited by a noise level of
electronic components. As an example of this problem, the
modern femtoampere amplifier LMP7721 by Texas
Instrument which has typical input bias current at 3 fA and
input-referred current noise at 0.01 pA/Hz-1/2. For a current
detection limit at 10 fA the measurement bandwidth reaches
(current detection level/input current noise)2 =1 Hz, i.e. time
resolution for measurements is 1 s, amount of electrons for
detection by the amplifier is greater than 6 000 electrons.
So the physical limit of modern electronics is greater than a
single electron detection level for a real potentiostat circuit.
Electronic elements as wires, semiconductors chips,
resistors, and others have electronic noises which specify a
detection level in an electrical circuit, and its reduction to
absolute zero level is practically impossible.
On the other hand, the utilization of novel construction
technics and measurement methods can overcome limiting
factors. In this paper, we try to analyze the construction of a
tradition potentiostat to decrease the response time to
nanosecond resolution and to determine sensitivity which
we can obtain with commercial operational amplifiers.
Investigations of possibilities to construct an ultrafast
potentiostat as well as its utilization were considered in
different articles [2-20]. Th więcej »

Renewable energy sources are now considered to be
the most prospective energy sector. Solar energy and its
derivatives are a free and inexhaustible source of energy
[1]. Thanks to the rapid development of technologies in the
field of renewable energy, the efficiency of generating units
increase year by year, while the investment cost decrease.
Increasing the share of renewable energy sources in the
energy systems of the Member States is now a priority in
the European Union energy policy. Funds earmarked for
this purpose are to accelerate the development of
renewable energy sources and enable diversification of
fuels and gradual independence from conventional fuels.
The current climate package assumes an increase in
renewable energy sources share in the European Union to
20% by 2020. In 2016, the share of renewable energy in
final energy consumption was 17% for the European Union
[2]. Another target will be to increase energy production in
renewable energy sources to 27% in 2030 [3].
According to the data of the Polish Energy Regulatory
Office [4], in the Polish national power system, the total
installed capacity in renewable energy sources at
30.05.2018 amounted to 8 584,552 MW, and the power in
installations using wind energy was 5 874,778, which is
68,43% of the total installed power in renewable energy.
One can notice the slowdown in the development of wind
energy in Poland as a result of the Wind Farm Investment
Act [5,6]. In 2016, the installed capacity in wind sources
was 5 807,416 MW, so within 2 years the power increased
by only 67,362 MW.
The high installed capacity in wind farms makes it
possible to use them for the process of voltage regulation in
the power system nodes. Thanks to the use of wind farms
with large reactive power control options, the transmission
system operator can use wind farm to maintain the required
voltage level at the connection point [7]. The use of wind
farms in the reactive power contro więcej »